1. Field of the Invention
The invention generally relates to apparatus for advancing a transducer with respect to a rotated disk to record and/or play back information on the disk. More particularly, the invention relates to an improved indexing mechanism for the transducer, which substantially prevents any roll of the transducer about an axis defining the direction of travel of the transducer relative to the rotated disk.
2. Description of the Prior Art
Magnetic disks for storing information have been available for several years in the form of "floppy" flexible disks typically made by coating one or both faces of a thin, highly flexible sheet of polymeric or other plastic film with magnetic oxide. This limpy flexible disk is usually permanently enclosed within a close-fitting, protective outer envelope, in which the disk is freely rotatable. The envelope has an enlarged central opening for access to a hub at the center of the disk to rotate the disk. A radical slot opening is provided in the envelope to permit a magnetic head to access a magnetic-oxide coated face of the disk as the disk is rotated. The magnetic head is translated radially across the face of the disk in incremental steps to predetermined positions, each of which corresponds to an individual narrow, closely spaced, circular recording track on the disk.
A common form of an indexing mechanism for advancing a magnetic head radially from track to track on a rotated disk comprises a carrier which supports the magnetic head and a guide along which the carrier is translated. As depicted in U.S. Pat. Nos. 3,665,433 and 3,721,967, the carrier may take the form of a wheeled carriage and the guide may take the form of rails or grooves for supporting the wheels of the carriage. Often, for example in U.S. Pat. Nos. 3,969,768 and 4,012,791, a lead screw is threadedly engaged with the carrier. A stepper motor rotates the lead screw in incremental steps to move the carrier and the magnetic head. Because the magnetic head is positioned in alignment with the successive recording tracks on the rotated disk, it is especially important that the head be precisely located with respect to the tracks, and that it be accurately held in place at each track. However, a problem existing in prior art indexing mechanisms is that rotation of the lead screw can cause the carrier to roll slightly about its travel axis. This will result in a similar rolling of the magnetic head relative to the recording tracks on the rotated disk. Consequently, the head-to-disk position may be changed from the preferred angle, causing some signal drop-off.